Global warming: Design of a flow-through shallow lake mesocosm climate experiment

Abstract

Shallow lakes are likely to be strongly impacted by climate changes and, in particular, by increased temperatures. To enable realistic experimental studies of the effects of higher temperatures on in-lake processes and dynamics, technologically advanced systems are required. This paper presents design details, operating characteristics, and background information on a currently operating experimental flow-through mesocosm system that allows investigation of the interactions between simulated climate warming and eutrophication and their impacts on biological structure and ecosystem processes in shallow lakes. We use 24 mesocosms to combine three temperature scenarios (one unheated and two heated relative to the Intergovernmental Panel on Climate Change climate scenario A2 and A2 + 50%, respectively) and two nutrient levels (enriched and nonenriched). Planktivorous fish (male sticklebacks, Gasterosteus aculeatus) are stocked in accordance with the nutrient level. The water residence time is regulated by the semicontinuous addition of water and is approximately 2.5 mo in each mesocosm. For heating, we use electrically powered heating elements. The heating system has performed well over 16 mo of continuous heating, and seasonal and diurnal temperature variations of the unheated reference mesocosms were paralleled well by the heated mesocosms. The performance of the flow-through system and the heating technique are discussed with special emphasis on strengths, limitations, and potential improvements of the system. To illustrate the performance of the system and its potential, we present data for selected periods on total phosphorus retention in the mesocosms and system primary production and respiration.

An automatically operated system for simulating global change temperature and ultraviolet B radiation increases: application to the study of aquatic ecosystem responses in mesocosm experiments

“…4d, April 4, 11, and 12). Liboriussen et al (2005) described a global warming mesocosm experiment where the experimental water was heated, relative to the unheated reference mesocosms, under low and high warming scenarios, according to the IPCC climate models A2 and A2 + 50%. In the temperature-regulating system presented in our study, the temperature target can similarly be modified in real time to reproduce predicted environmental models, if the planned targets are compatible with the regulation constraints.…”

“…Several investigations using mesocosms have demonstrated the effects of UVBR on the structure and function of the aquatic food web (Belzile et al 1998;Mostajir et al 1999;Chatila et al 1999 and2001;Fauchot et al 2000;Mousseau et al 2000;Gustavson et al 2000;Whitehead et al 2000;Wängberg et al 2001;Fouilland et al 2003;Bouchard et al 2005;Ferreyra et al 2006; see also Belzile et al 2006 for a synthesis of UVBR studies performed in mesocosms). Other mesocosm studies have focused on increases in temperature (Keller et al 1999;Baulch et al 2003;Baulch et al 2005;Liboriussen et al 2005) and demonstrated effects on the entire aquatic food web, both pelagic and benthic compartments. It is clear, however, that although mesocosms can be a powerful tool to study the effects of various environmental factors on the whole food web structure and function, the experimental design must be as realistic as possible in simulating the forcing factors and imitating their short-term variability.…”

“…One is the capacity of the experimental system to reproduce the differential increases in monthly temperatures that are predicted by the various global warming models, as described in Liboriussen et al (2005). The other factor to consider is the capacity of the system to respond to short-term temperature fluctuations.…”

“…For example, in shallow waters such as lagoons, water temperature is influenced profoundly by prevailing air temperature and, therefore, exhibits diel and short-term fluctuations. Recently, various different designs for land-based mesocosms have been used to investigate the effect of climatic warming on lake ecosystems (Baulch et al 2003;Liboriussen et al 2005). Baulch et al (2003) used a hot water circulation system to increase temperature in mesocosms open to the sediments.…”

“…Baulch et al (2003) used a hot water circulation system to increase temperature in mesocosms open to the sediments. Liboriussen et al (2005) used heating elements immersed in land-based flow-through mesocosms. The latter system improved sensitivity and accuracy of the temperature increases by using electrical heaters.…”